1. Field of the Invention
The present invention relates to a laser light deflection amount detecting apparatus that detects the amount of deflection of laser light in two directions orthogonal to the optical axis of the laser light, a displacement measuring apparatus including the laser light deflection amount detecting apparatus, a method for manufacturing a mold for molding an optical element, and an optical element.
2. Description of the Related Art
Machining by means of a machine tool requires information on the positions of tools on the machine tool and on the shapes of cutting edges of the tools. One method for acquiring, by measurement, the information on the positions of the tools and the shapes of the cutting edges of the tools is to acquire tool information (the positions of the cutting edges and the shapes of the cutting edges) on the machine tool in a noncontact manner by irradiating the tools with laser light and measuring the amount of light having passed the tools without being blocked by the tools. This measurement method eliminates the need for dummy processing otherwise required to acquire the tool information by measurement. This advantageously increases throughput by an amount corresponding to a time required for the dummy processing and prevents the tools from being worn away during the dummy processing. However, the displacement measurement method of measuring the amount of light having passed a measurement target without being blocked by the measurement target may suffer deflection of the optical axis of laser light, leading to a measurement error.
Thus, a quadrisected four photo diode is conventionally used to measure the amount of deflection of laser light in two directions orthogonal to the optical axis of the laser light in order to correct the deflection of the optical axis of the laser light (Japanese Patent Application Laid-Open No. H06-60404). The quadrisected photo diode includes four light receiving elements. The amounts of light received by the respective elements are referred to as A, B, C, and D. The amount of deflection of the optical axis in one of the two directions is determined based on the result of the calculation of A+B−(C+D). The amount of deflection of the optical axis in the other direction is determined based on the result of the calculation of A+D−(B+C).
However, the method of measuring the deflection of the optical axis using the quadrisected photo diode is limited in resolution by the number of pixels in the quadrisected photo diode. The method thus has difficulty accurately measuring the deflection of the optical axis of laser light. That is, the amount of deflection in each of the two directions is determined by addition and subtraction of the results of light reception carried out by the four light receiving elements. Thus, errors in the measurement by the four light receiving elements are accumulated in the determined amounts of deflection. Consequently, accurately measuring the amounts of deflection of the laser light in the two directions is difficult.
Thus, an object of the present invention is to provide a laser light deflection amount detecting apparatus that can accurately detect the amount of deflection of the optical axis of laser light in two directions orthogonal to the laser light, a displacement measuring apparatus including the laser light deflection amount detecting apparatus, a method for manufacturing a mold for molding an optical element, and an optical element.